1979 mustang problems with carb i think

i just bought this car off someone they say it has a 289 bore 30 over i think its a 302 bore 30 over im havin problems with it also it came with a holly 650 with elc choke it would stall when i put it gear or give it gas so i took it off to rebuild it and put a edelbrock on there till the holly was rebuilt and now the motor is backfirein i found out that the holly carb primary butter flys were not closein all the way what should i do should i get a new holly or edelbrock? and how can i find out what motor is it everything is aftermarkit it came with a stright 6 and was manual and now auto